As shown in FIG. 1, in the case of a positive system (the combination of a resist composition and an alkali developer) for the pattern formation, only a material of performing the pattern formation by selectively dissolving and removing a region having strong light irradiation intensity out of spatial frequencies of an optical image is provided. On the other hand, as for a negative system (the combination of a resist composition and an organic solvent-containing developer), only a material system of performing the pattern formation by selectively dissolving and removing a region having a weak light irradiation intensity is provided.
The term “alkali developer” as used herein indicates a developer that selectively dissolves and removes the exposed area not lower than a predetermined threshold value (a) shown by a solid line in FIG. 1, and the “organic solvent-containing developer” indicates a developer that selectively dissolves and removes the exposed area not higher than a predetermined threshold value (b). A development step using an alkali developer is called an alkali development step (sometimes referred to as a positive development step), and a development step using an organic solvent-containing developer is called an organic solvent-based development step (sometimes referred to as a negative development step).
Meanwhile, JP-A-2000-199953 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) describes a double development technology as the double patterning technology for raising the resolution. In this case, an image forming method by general chemical amplification is utilized, and by making use of a property that upon exposure, the polarity of a resin in a resist composition becomes a high polarity in a region irradiated with high-intensity light and a low polarity is maintained in a region irradiated with low-intensity light, development is performed by dissolving a high exposure region of a specific resist film with a high-polarity developer, while development is performed by dissolving a low exposure region with a low-polarity developer. More specifically, the region not lower than an exposure dose E2 of irradiation light 1 in FIG. 2 is dissolved using an aqueous alkali solution as the developer, the region not higher than an exposure dose E1 is dissolved using a specific organic solvent as the developer, and, as shown in FIG. 2, the region at a medium exposure dose (E2 to E1) is allowed to remain without being developed, whereby a line-and-space pattern 3 with a pitch half the pitch of the exposure mask 2 is formed on a wafer 4.
European Unexamined Patent Publication No. 1,939,691 discloses organic solvent-based development and a pattern forming method by double exposure and double development using organic solvent-based development.
In the pattern forming method using an organic solvent-containing developer, which can be utilized for the formation of a fine pattern, it is demanded to suppress defects produced after the development step.